1. Field of the Invention
The present invention relates to a pulsation suppression device for a pump. A pulsation suppression device of this type is used for suppressing pulsation (pulsative pressure) of a discharge pressure which is produced by variation in the flow rate or the pressure when a reciprocal pump is operated. Therefore, the pulsation suppression device of the present invention may be interposingly used in a liquid transporting pipe through which various processing chemical liquids such as a washing liquid used in a semiconductor production step, specifically, a surface washing liquid for washing an IC or a liquid crystal device is transported by a reciprocal pump.
2. Description of the Prior Art
As a pulsation suppression device for a pump of this type, a device having a configuration which is disclosed in, for example, Japanese Patent Publication Laying-Open No. 8-159016 is known. The proposed pulsation suppression device has a liquid chamber and a gas chamber which are separated from each other by an extendable and contractible barrier such as a bellows or a diaphragm. In the pulsation suppression device, the liquid chamber has a role of temporarily storing the liquid (such as the chemical liquid) to be transported by a reciprocal pump, and the gas chamber has a role of being filled with a gas for suppressing pulsation. The capacity of the liquid chamber is changed by means of extension and contraction of the diaphragm so as to maintain the pressure balance between the liquid chamber and the gas chamber, thereby suppressing pulsation of the discharge pressure of the reciprocal pump.
The pulsation suppression device further has a gas supply and discharge switching valve mechanism. The switching valve mechanism is provided with a function of, in accordance with a change in the capacity of the liquid chamber, being alternately switched to a normal mode in which the gas is not supplied to nor discharged from the gas chamber, a gas supply mode in which the gas is supplied to the gas chamber, and a gas discharge mode in which the gas is discharged from the gas chamber. These modes are switched over by means of a reciprocal operation of an operating rod interlocked with extension and contraction of the diaphragm.
According to the known pulsation suppression device pulsation of the transported liquid due to the discharge pressure of the pump can be suppressed by means of a change in the capacity of the liquid chamber which is caused by extension and contraction of the diaphragm, and also the change in the capacity of the liquid chamber can be suppressed to a low degree by the gas chamber pressure adjusting function of the gas supply and discharge switching valve mechanism.
All conventionally used pulsation suppression devices has the following problem. In an example case where such a pulsation suppression device is accidentally operated under a condition where the gas is not supplied to the gas chamber, when the pressure of the transported liquid is abnormally raised, the pressure balance between the liquid chamber and the gas chamber is broken and the diaphragm abnormally extends. A closed end face of the thus extending diaphragm strongly collides with an end portion of the operating rod which is a part disposed in the gas chamber. This collision may cause the closed end face of the diaphragm to be deformed or damaged. In some cases, an excessive force may be applied also to the operating rod, so that the operating rod is deformed or broken. When such a situation occurs, there arises a fear that the subsequent operation will be hindered and the expected pulsation suppression function cannot be exerted. Depending on the degree of the damage of the closed end face of the diaphragm, furthermore, a serious situation where the transported liquid such as a chemical liquid leaks to the outside may occur.
In order to enhance the pulsation suppression function of a pulsation suppression device of this type, it is effective to increase the internal capacity of the gas chamber. When the gas chamber is elongated in the extension and contraction directions of the diaphragm in order to increase the internal capacity of the gas chamber, however, the axial length of the operating rod which is reciprocally operated in the extension and contraction directions of the diaphragm in interlock relationship with extension and contraction of the diaphragm must be increased. When the operating rod is elongated in this way, the operating rod is easily inclined, or a spring which is used for urging the diaphragm in the contraction direction is hardly maintained to a suitable shape. This causes a fear that the operation direction of the operating rod fails to coincide with the extension and contraction directions of the diaphragm. When such a situation occurs, the reliability of the operation of the gas supply and discharge switching valve mechanism is lowered, or the operation itself is not adequately conducted, thereby causing a fear that the expected gas supplying and discharging action of the gas chamber cannot be correctly performed.